Question Details

The product of all positive real values of x satisfying the equation x16(log5x)368log5x=516 is ___________ .

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Correct Answer :

1

Solution :

The correct answer is 1.

We are given the logarithmic equation:

x16(log5x)368log5x=516

To solve for x, let us take the logarithm to the base 5 on both sides of the equation.

log5(x16(log5x)368log5x)=log5(516)

Using the power property of logarithms, logb(ak)=klogb(a), we can bring the exponents down:

(16(log5x)368log5x)·log5x=16

Let us make a substitution to simplify the equation. Let:

t=log5x

Substituting t into the equation gives:

(16t368t)·t=16

Expanding the left side yields:

16t468t2=16

Rearranging all terms to one side to form a polynomial equation:

16t468t2+16=0

We can divide the entire equation by 4 to simplify the coefficients:

4t417t2+4=0

This is a quadratic equation in terms of t2. We can factor it by splitting the middle term:

4t416t2t2+4=0
4t2(t24)1(t24)=0
(4t21)(t24)=0

This gives us two cases for t2:

1) 4t21=0t2=14t=±12
2) t24=0t2=4t=±2

Thus, the four real roots for t are t1=2, t2=2, t3=12, and t4=12.

Since t=log5x, we have x=5t. The corresponding values of x are:

x1=52
x2=52
x3=51/2
x4=51/2

Now, we find the product of all positive real values of x:

P=x1·x2·x3·x4
P=52·52·51/2·51/2
P=522+1212
P=50=1

Hence, the product of all positive real values of x is 1.

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